1. Field of the Invention
The present invention relates generally to apparatus for performing electrophoresis, and in particular, to an apparatus in which gel slabs are supported on a gel slab platform in the vertical position in conjunction with the necessary buffer solutions for the electrophoretic separation of samples.
2. Related Art
Numerous electrophoresis devices have been developed since the discovery that charged particles suspended between opposite poles and in an electric field migrate toward the pole possessing the charge opposite that the particle. The extent of migration is an indication of the composition of the particles.
Many apparatus have been designed to facilitate gel electrophoresis of biologically significant macromolecules. Some apparatus are designed so as to orient the gel vertically; others are designed to orient the gel horizontally. A vertical orientation has been generally found to be preferred for the electrophoresis of nucleic acids in such applications as nucleic acid sequencing.
Apparatus designed to facilitate the electrophoretic separation of DNA or RNA fragments generated as part of nucleic acid sequencing procedures share a number of elements. These common elements include; a gel slab composed of two flat glass plates separated by thin strips placed at opposite edges and between these plates enclosing a gel composed of polyacrylamide cast between the plates within which the electrophoretic separation will be carried out; a vertically oriented support platform to which the gel slab can be secured; means for securing the gel slab to the support platform; two reservoirs for containing buffer, one installed toward the upper end of the vertical slab support and a second installed toward the lower end of the vertical slab support; and an electrode installed in each reservoir to apply a voltage to buffer added to the reservoir. Placement of the gel slab against the vertical platform situates the gel so that when buffer is added to each of the reservoirs and an effective electrical contact is established between the buffer in one reservoir and the buffer in the other reservoir through the gel to be used to electrophoretically separate the components of the test samples. Owing to the geometry of this assembly, most of the voltage difference between the electrodes occurs within the gel.
The usual practice of electrophoresis as applied to nucleic acid sequencing requires an apparatus constructed to hold a gel slab typically measuring from 200 to 400 inches square (one dimension is usually no larger than 4 times the other dimension). Gel slabs of this size require the use of heavy gauge glass plates. Further, when electrophoretic separation is carried out substantial heat is generated in the gel slab. This heat is conveniently removed by placing a large conducting plate in contact with the gel slab, most conveniently, by incorporating this plate as part of the vertical platform against which the gel slab is placed. Consequently such apparatus tend to be heavy and difficult to carry. As a practical matter electrophoresis of this type require the application of high voltages between the buffer reservoirs; voltages which present a danger of accidental electrocution, to users of the apparatus. As a further practical matter most nucleic acid sequencing procedures require the addition of hazardous quantities of radioactive materials to the gel and the subsequent contamination of the buffer contained in the reservoirs, particularly the buffer in the lower reservoir, with radioactive material. All these considerations make convenience, transportability, ease of cleaning, and safety important to users of this type of apparatus.
Furthermore, most known electrophoresis apparatus are often constrained to a certain height. Thus, if electrophoresis runs of different lengths were desired to be performed, separate apparatus have to be purchased for each run length. This multiple purchasing of different apparatus adds to cost. It is therefore desirable to have a vertical gel slab electrophoresis apparatus which has an adjustable height, and which still runs electrophoretic separations reliably, regardless of the height of the assembled apparatus.